TRANSACTIONS OF THE SKCTXONS. 97 



13 subjected in summer expending itself in producing evaporation, and not reacbing 

 the depths beneath. 



In the Eastern basin of the Meditei-ranean, the axis of which is about 2° further 

 south than that of the AVestern, the constant temperature, as determined by two 

 very deep soundings (one of them extending to more than 1900 fathoms) is 5^°, 

 which seems to represent its isocheimal, — this basin being cut otf from the intrusion 

 of any colder water, except the comparatively small quantity that may come down 

 into it from the Euxine. 



Now one marked consequence of this uniformity of Temperature in the deep 

 Mediterranean basins, from 100 fathoms downwards, wiU be an absence of that 

 Vertical Circulation, which, in the Oceanic areas, brings eveiy drop of water at 

 some time or other into contact with the Atmosphere, and thus effects its aeration, 

 — the excess of Carbonic Acid which it has derived from Animal Respiration, and 

 from the Decomposition of Organic matter, being removed, and replaced by Oxygen. 

 Hence, if the whole of the deeper water of the Mediterranean is in a state of 

 stagnation, it might be expected to become highly charged with Carbonic Acid (its 

 Oxygen being proportionately reduced), through the decomposition of the large 

 quantity of Organic matter brought down by the great rivers,— especially the Nile 

 in the Eastern basin, and the Rhone in the Western. This has been found by the 

 Author to be really the case— the percentage of Carbonic Acid in the entire amount 

 of gas set free by the boiling of abyssal water in the Mediterranean being as high 

 as GO, and that of Oxvgen as low as 5, that of Nitrogen being 35 ; whilst the highest 

 percentage of Carbonic Acid ever met with in the abyssal water of the Atlantic was 

 48, that of the Oxygen being IG. Thus it appeared that nearly the whole available 

 Oxygen, in the abyssal water of the Mediterranean, had been used up by the de- 

 composition of Organic matter ; and this condition was quite sufficient to account for 

 the extreme paucity of Animal life in the muddy deposit which is being formed by 

 the very slow subsidence of the finest particles brought down by the great rivers 

 and diifused through the entire mass of Mediterranean water. 



Thus any deposit formed in a deep Inland Sea which is cut off from all but super- 

 ficial communication with the Ocean outside, and into which a large quantity of 

 Organic matter, as well as of Mineral sediment, is brought by large rivers, might be 

 expected to be nearly or entirely azoic — Edward Forbes's limitation of Animal life 

 to 300 fathoms being generally true of the Mediterranean, though not of the open 

 Ocean. 



The Temperature of the Red Sea is probably higher throughout than that of any 

 other Inland sea, — the surface-temperature of its Northern part, even in January and 

 February, being never beneath 70°, whilst in the Southern it rises in July and 

 August sometimes to nearly 90°, and the Strait of Babelmandeb beinp: so shallow 



gave a wiifurin feinpt 

 Hence it may be assumed with tolerable certainty, that even in the deepest part of 

 tlie Red Sea", where the bottom lies at more than 1000 fathoms, the temperature 

 •n-\]\ be never lower than 70° — thus contrastino- very strongly with the temperature 

 of the lower stratum of the Arabian Gulf, which, having a temperature of about 

 36°, must have come all the way from the Antarctic Sea. — In connexion with this 

 high temperature of the Red Sea, it may be suggested as deserving of inquiry, 

 whether the reef-building Corals live at a gTeater depth in it, than they do in the 

 Tacilic. 'J'he inquiries of Dana fully confirm the statement of Darwin, that these 

 Corals do not live at greater depths than 20 fathoms ; and they have also led him 

 to the conclusion that they are limited in their distribution by the isocheimal of 

 68°. Now the question arises whether the limitation of Depth is not really cleter- 

 mined by Temperature ; and in that case these Corals should be found living in the 

 Red Sea at greater depths than in the Pacific. 



A curious contrast to this, however, is afforded by the Sulu Sea, an area lying 

 between the N.E. portion of Borneo and Mindinao, only partly enclosed by islands 

 at the surface, but shut in beneath by reefs which connect them. Now the surface- 

 temperature of this sea, like that of the China Sea in its neighbourhood, is from 

 80° to 84° 5 and the temperature of both seems to fall at about the same rate through 



